The goal of this R21 proposal is to complete the preclinical development and evaluation of an instrumented replacement trapezium (iTrapz) capable of measuring joint contact loads at the base of the thumb, establishing the rigor for a future clinical trial in trapezial arthroplasty. The numerous surgical treatments for late-stage osteoarthritis (OA) of the thumb carpometacarpal (CMC) ? or trapeziometacarpal (TMC) ? joint, are highly varied and suboptimal. TMC OA is a degenerative disease that results in significant impairment due to pain and loss of function. The prevalence of TMC OA is at least 20-25% in those over 50, and it increases into the eighth decade when as many as 80% have evidence of disease. High forces in the trapeziometacarpal joint are believed to influence OA development and treatment success. However, our understanding of joint loads developed in the hand is limited to predictions from mathematical models that have yet to be validated by in vivo measurements. Custom implants instrumented to measure joint contact loads have been developed for the hip, knee, and spine. Data from these implants has provided critical insight into joint function, with the tangible direct benefits of validating and improving musculoskeletal models and providing important information for implant designers and manufacturers. Instrumented implants also have the potential to provide highly novel biofeedback to patients to guide rehabilitation. Building on our extensive and rigorous in vivo studies of TMC morphology and kinematics, and the records of success in other instrumented joints, we propose to develop and validate a preclinical instrumented trapezium implant, which we refer to as the iTrapz. In our first aim we will design, fabricate and validate a proof-of-concept wired iTrapz. In Aim 2 we will validate the wired iTrapz in a cadaver model using a robotic musculoskeletal simulator. Once we complete these aims we will have a highly innovative load sensor suitable for cadaver studies. Given the need for more rigorous studies of thumb arthroplasties, this accomplishment alone will have a significant impact. In Aim 3 we will develop a first-prototype inductively powered and telemeterized iTrapz implant. In Aim 3 we will also begin planning for in vivo implementation in a clinical study. Upon completion of Aim 3 we will have demonstrated that measuring in vivo thumb loads during the activities of daily living is feasible, and we will have developed the necessary knowledge, skills and technologies to support the fabrication of a hermetically sealed implant suitable for clinical implementation. This project is significant in that it will benefit several constituencies: clinicians will benefit from the knowledge of the loads associated with disease, injury, surgery and repair; the modeling and research communities will benefit directly from measurements of joint loads during activities of daily living, which are unknown in the hand; and engineers and manufacturers will benefit from critically-needed performance data.